Method and means for starting a recording drum



Feb. 15, 1966 J. P. wooos ETAL METHOD AND MEANS FOR. STARTING ARECORDING DRUM Filed April 16, 1963 Edw/n B.

2 Sheets-Sheet 1 1N VENTORS. John R Woods Will/gm M. Mull/figs ATTORNEYUnited States Patent Claims. (Cl- 19284) The present invention relatesto a means for starting a' recording drum. More specifically, theinvention relates to a means for increasing clutch speed and reducingslippage so that the timing of events during recording can be reliablyreferred to a starting point and various recordings can be added withoutadjusting for starting time variations.

It is general practice in the recording art to initiate drum rotationwell ahead of recording time. For example, in seismic field recorders itis conventional to initiate drum rotation prior to actuating the chargedetonation switch. This insures the drum sufiicient time to reachconstant recording speed before significant data is recorded. Usually inthis case each geophone group is provided with an individual recordinghead, and the contains a group of 64 seismometers. The surface of theground between the seismometer groups is divided up into a number ofequal intervals. The weight truck starts dropping at the first interval;and each time the weight drops, the response of seismometer group 1 isrecorded on one channel and the response of seismometer group 2 isrecorded on another channel. Five drops are made along each interval,giving a total of ten recordings on ten channels. The truck then movesto the second interval and makes five drops along that interval. Afterthe completion of these drops, an addition of the magnetic channels ismade with the reflection events aligned. The ten recordings made byseismometer group 1 are added and rerecorded as a single channel. Theten recordings of seismometer group 2 are then added and rerecorded as asingle channel. The weight truck then proceeds to the next interval andrecords five more drops. If a 50 percent ground overlap is desired, theoriginal five recordings made by seismometer group 1 from the secondinterval are added to the five recordings made at the third interval andrerecorded as a second composite rerecording of group 1. The originalrecordings of group 2 over the second and third intervals are also addedand rerecorded on a single channel. This procedure continues until thedesired area is traversed. It is obvious from this example that thelarge number of additions and rerecordings presents a recording andsynchronizing problem not found in conventional type recordingtechniques. For additional information concerning this method ofcomparing signals, see copending application, Serial No. 775,491, nowPatent No. 3,078,947, owned by a common assignee. Since a number ofrecordings are to be added, the starting time of each record must beinitiated from the same reference point or reference time. If this isnot done, the variations from a standard or reference starting time(caused.

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by variations in starting lag, clutch slippage, etc.) must be subtractedor compensated for in someway before the recordings can be added. Put inanother way, the records to be added must be lined up from a zero timeor the individual starting time variations must be subtracted from eachrecord before the records can be added and rereconded on a singlechannel.

From the above discussion it is clear that the desired method ofoperation is to start all the recordings from the same zero referencetime instead of individually adjusting for starting time variations. Itis also obvious that it is highly desirable to accomplish the above withthe minimum change in conventional recording equipment. By eliminatingvariations in starting lag in conventional recording equipment, not onlycan the weight dropping technique be utilized, but conventionally maderecords can be combined as desired.

Since most conventional recording systems utilize a drum, the recordingtime for each channel can be varied to a certain extent depending on thecircumference of the drum and speed of rotation. However, practicallimitations in geophysical work dictate that the recording time for eachchannel be approximately five seconds. This time limit necessitates anew channel for each drop in order that the desired depth reflectionsmay be recorded. In order to conserve the channel for recordinginformation instead of wasting a portion by starting the drum beforereflected signals are received, the recording drum rotation is initiatedat or about the time the source of energy is actuated. This can beaccomplished by a radio wave created by an impulse switch located on aweight or by a signal from a blaster. Drop initiation solves therecording space problem in a somewhat conventional manner; however, theproblem of automatically accelerating the recording drum from astationary position to recording speed with a minimum, uniform' timedelay has not been satisfactorily solved by any device or method knownto applicants.

It is an object of this invention to provide a means to insure thatrecording drum rotation is initiated in such a manner that the drumstart-to record speed time relay is always equal.

Another object is to provide a means to insure a minimum and uniformtime delay in driving a recording drum to recording speed.

Another object of this invention is to provide a means to insure aquick-acting, nonslipping clutch engagement.

An additional object of this invention is to provide a means to insurethat various channels recorded on a recording drum may be added withoutadjusting for starting time variations.

Another object of this invention is to provide a means for initiatingrecording drum rotation on command in such a manner that it attainsrecording speed in not more than 10 milliseconds effective record time(,the time required to establish positive contact with ring 10).

Another object of this invention is to provide a means for monitoringthe initiation of recording drum rotation to see that it attainsrecording speed in not more than 10 milliseconds effective record time.

Another object of this invention is to provide a means to accomplish theabove-listed objects with a minimum of changes to a conventionalgeophysical recording system.

Another object of this invention is to provide a means to accomplish theabove-listed objects which also can be used in conventional geophysicalrecording.

Briefly described, the invention consists of a means for automaticallystarting and accelerating a recording drum to record speed with aminimum and uniform time delay so that the timing of events on a numberof recordings can be reliably referred to a common reference point. Thenovel system accomplishes this by reducing clutch slippage bycontinuously rotating a high mass clutch at recording speed, engagingthe clutch with a low mass stationary body compliantly coupled to arecording drum, accelerating the drurn'to recording speed, anddecreasing clutch-locking time by driving a light-weight engagingelement or clutch face with a force of large magnitude. One form ofapparatus capable of carrying out applicants novel method includes afast-acting magnetic clutch, a compliant coupling, and an accelerator orfollow-up mechanism. The magnetic clutch engages a drive pulley to arecording drum through a compliant coupling. The compliant couplingconnecting the magnetic clutch and the recording drum serves as aninertia-absorbing linkage to prevent clutch slippage. The accelerator orfollow-up mechanism causes the recording drum to attain recording speedin a minimum time and in a uniform manner before the compliant couplingis expanded to its limit.

FIGURE 1 shows an isometric view, partially in cross section, of oneform of the automatic high speed magnetic clutch-accelerator mechanism.

FIGURE 2 shows the operational sequence and a sample record plotted on atime base.

Referring to FIGURE 1, recording drum 1 is mounted on shaft 2. Plate 3,which for ease of assembly is initially separate from drum 1, ispositioned on shaft 2 and secured so that drum 1, shaft 2 and plate 3rotate as a single unit. Drive pulley 4 continually rotates housing 5(permanent magnet) by means of a thin, steel belt 6 around itsperiphery. Pulley 4 can be mounted on the shaft of a synchronous motoror other type driving means. Arrnature 7 (aluminum or other nonmagentic,lightweight material) is caused to rotate with housing 5 by means ofsmall pins 5', which allow axial movement of the armature with respectto the housing. The armature is provided with electrical windings 8,which are located within the air gap of the magnetic circuit of thehousing, and a clutch face, which is parallel to and adjacent ring 10.Slip rings 9 allow the windings to be energized. Ring 10 (Bakelite orother low mass material) is coupled to plate 3 by compliant couplingspring 11 (unidirectional coupling by virtue of pin 17 seated againstthe far end A of notch 18). Pin 17 and notch 18 control the amount ofmovement between ring 10 and plate 3, as well as the expansion of spring11. The drum kick or accelerator mechanism includes spring 12 mounted onthe end of pawl 13, which engages catch 14 mounted on the side ofdrum 1. Latch 15 is held on catch 14 by the tension of spring 19.Solenoids 16 are positioned under latch arm 15 and are electricallyconnected to the same voltage source as windings 8.

In operation, a driving means, not shown, rotates pulley 4 and housing 5at the desired recording speed. When a weight, not shown, is dropped, animpulse switch attached to the top of the weight closes at impact,causing a time-break to be propagated over a radio link to a recordingtruck. This type or similar impulse can be used to automatically closeillustrative switch 20 and start the recording drum. The illustrativeswitch can be any suitable switching means operatable by the radio linkor the particular communications used between the weight dropping truckand the recording truck. The closing of switch 20 causes a large currentto be sent through slip rings 9, energizing windings 8 and causing theclutch face of armature 7 to slide to the right on pins 5 and to lock onto ring 10 in such a manner that ring 10 reaches recording speed withinapproximately 3 milliseconds. This is accomplished in the followingmanner. The large current through windings 8 sets up a magnetic field inopposition to the field set up by permanent magnet 5. (In order toincrease the clutch reaction time, a high amplitude voltage pulse isadded to the initial clutch exci tation voltage.) This oppositionquickly forces armature 7 axially against ring 10. Ring 10 is made of alow mass material, such as aluminum or Bakelite, to reduce the inertialefiect and to insure minimum slippage between periphery.

rotating armature 7 and the ring. A rubber facing on armature 7 and fineabrasive dust embedded on the face of ring 10 may also be provided toreduce slippage if desired. As ring 10 begins to rotate, tension isapplied to spring 11, which couples plate 3 and the recording drum 1 toring 10. Spring 11, connecting ring 10 and plate 3, is of sufficientstrength to overcome bearing friction and recording element friction incontact with the drum It should be noted that spring 11 must besufficiently strong to urge pin 17 against the far end A of notch 18after the kicking action has overcome drum inertia. If 17 is notmaintained against end A, it will float between the ends A and B ofnotch 18, causing errors in the timing lines.

At the same time the high speed, magnetic clutch is energized, solenoids16 are energized, automatically releasing latch 15 and allowing spring12 t o,expand, im-

parting an initial kick or accelerating force to drum 1- by pawl 13.Because of the mechanical action required after the solenoid activation,the drum is not accelerated simultaneously with the clutch action.However, the accelerating force is designed to impart sufficientacceleration to the drum so that the lag b tween the drum and thearmature 7 (and ring 10) is e iminated before coupling spring 11 isstretched far enough to allow pin 17 to reach the near end B of notch18. Spring 12 should be limited in strength to prevent overdriving pin17 during the kicking action. If pin 17 is ovei'dn'ven, it will strikeits seating position (end B) too hard and cause clutch slippage in areverse direction.

After pawl 13 has applied an accelerating force to drum 1, it extendsunder and to the left of 14 until the recording cycle is completed. Theaccelerator is reset by reversing the direction of drum rotation causing14 to temporarily depress and move by 15 and compress spring 12 untilthe drum stops. In the meantime, the latch 15 under the tension .of 19rises and blocks the movement of 14. The system'is reset for the nextrecording cycle. In this manner pawl 13 of the drum accelerator means ismade to intermittently contact the drum.

With the operation of applicants invention in mind, reference is nowmade to FIGURE 2. This figure shows the operational sequence of drivingthe drum to record speed versus time. To better explain one use ofapplicants novel invention, a schematic of a seismic record is shownunder the sequence time plot. Since the time base is not drawn to scale,individual time increments are indicated by appropriate arrows. Amaximum time for establishing positive contact with ring 10 (timerequired for ring 10 to reach synchronous speed) is 10 milliseconds, buta more probable time is 3 milliseconds,

as illustrated. As shown in FIGURE 2, the operationis as follows: (a) attime 0, a weight strikes the ground, activating the clutch (and acounter, if used); (b) at time 0 plus approximately'.O03 second, ring 10(shown in FIGURE 1) reaches recording speed (a counter, if used, isrecording timingpulses 4, say, every .1 millisecond); (c) at time 0 plusabout .1 second, recording drum 1 (shown in FIGURE 1) reaches recordingspeed (the time required for the drum to reach constant speed is theminimum appearance time for reference pulse 1 and the minimum cutofftime for the counter, if used); (d) at time 0 plus about .2 second (orthe desired cutoff time), a counter, if used, cuts off and the referencepulse 1 is recorded; (e) at time 0 plus about .6 to .8 second, the firstseismic reflection is recorded.

Clutch slippage, if any, is experienced during the period time 0 secondsto about .003 second. The period between the reference point 1 (at, say,.2 second) and the seismic or other type signal received can beaccurately determined by conventional timing lines 2. Therefore, to addrecords, rerecordings are started from the refer ence pulse 1.

If desired, an electronic counter, or other type device, can be used tomonitor the ring engagement time. This is used primarily to determine ifthere is a change in the ring engagement time due to machine wear over along period of time or extreme changes in operating conditions. If sucha change did appear, the counter time would be used instead of .2 secondor the total elapsed time from 0 time to the appearance of the referencepulse.

In summary, to accomplish the objectives set forth supra, a method andapparatus have been devised by applicants to overcome or at leastminimize to a satisfactory degree clutch slippage so that the amount oftime in bringing the drum to recording speed is always uniform in amountor within the limits which can be tolerated in the system. In thegeophysical art this starting time variation should not exceed 1millisecond, because the desired record timing accuracy is at least 1millisecond. Since a practical system cannot be devised in which thereis no slippage or where the slippage is always the same, applicants havesolved the slippage problem by reducing to a minimum slippage causes andthe amount of time over which the remaining slippage occurs. In otherwords, a slippage of, say, 4 percent in a clutch system where theslippage .lasts for, say, 50.milliseconds may create an objectionabledrum lag. However, a slippage of, say, 4 percent over a period ofmilliseconds may not be objectionable. Applicants overcame the slippageproblem in the following manner:

(A) Reduce clutch slippage to a minimum. This is accomplished by:

(1) Reducing initial engaging inertial shock on the clutch by locking ahigh mass rotating body to a low mass stationary body.

(2) Overcoming friction inherent in the system by compliantly couplingthe low mass body to a recording drum.

(3) Reducing drum inertial shock on the clutch by independentlyaccelerating the drum.

(B) Reduce time required to engage clutch to a minimum. This isaccomplished by:

(l) Utilizing a fast acting engaging or clutch means to lock the movingbody with the stationary body.

Put in another way, a fast-acting clutch locks the revolving portion toa low mass body in a minimum of time; and the inertial and inherentfrictional effects of the machine are reduced by a compliant couplingand an accelerator which insures that the recording drum reaches thesynchronous speed of the clutch before sufiicient force is exerted onthe low mass body through the compliant coupling to cause clutchslippage.

From the foregoing it will be observed that applicants have devised anovel method and means for insuring a minimum uniform time delay instarting a recording drum. It is clear that the invention can be usedwith a conventional seismic recording system and that it enables such asystem to record signals created by the weight drop technique or tosimplify the addition of conventionally created signals. While only oneparticular apparatus has been illustrated and described, it will beapparent that further modifications will suggest themselves to thoseskilled in the art by the method described; and it is intended to coversuch modifications as fall within the scope of the appended claims.

We claim:

1. In a recording system of the class wherein recording operations arecommenced as a drum is accelerated from a stationary position, theimprovement comprising in combination.

(a) a rotatable recording drum means,

(b) a high speed clutch means,

(c) a compliant coupling means connecting said high speed clutch meansto said drum means,

(d) a drum accelerator means adapted to act independently of said clutchmeans and to contact and accelerate said drum means, and

(e) a switching means connecting said clutch means to said drumaccelerator means.

2. In a recording system as set forth in claim 1 wherein thehigh speedclutch means is a magnetic clutch and. the drum accelerator means is aspring actuated pawl.

3. In a recording system as set forth in claim 1 wherein the high speedclutch' means includes a rotating magnetic housing, a coil assembly, anda light weight armature supporting said coil assembly having a clutchsurface, said coil assembly movably mounted within and connected 'torotate with said magnetic housing.

4. In a recording system as set forth in claim 1 wherein the compliantcoupling means includes a spring, said coupling means being adapted tourge the recording drum means in a fixed relation with the high speedclutch means after said drum means is accelerated to full speed.

5. In a recording system as set forth in claim 1 wherein the high speedclutch-accelerator means is actuated automatically.

6. In a recording system as set forth in claim 1 wherein the drum meansincludes a means for limiting the movementof the compliant couplingmeans connecting the clutch means to said drum means.

7. An improved high speed magnetic clutch for a recording drumcomprising (a) a rotatable magnetic housing containing an indentation onone side thereof,

(b) a lightweight armature slidably connected to rotate with saidmagnetic housing,

(c) electrical windings mounted on a portion of said armature, saidelectrical windings positioned within said indentation, and

(d) a ring member rotatably connected to said magnetic housing andlocated adjacent one side of said armature.

8. In a device as set forth in claim 7 wherein a recording drum means isconnected to the ring member by a compliant coupling.

9. In a recording system of the class wherein recording operations arecommenced as a drum is accelerated from a stationary position, theimprovement comprising in combination (a) a recording drum connected bya compliant coupling to a clutch ring composed of nonmagnetic materialand having a first clutch surface,

(b) a rotatable high mass magnet,

(c) an armature slidably mounted adjacent and conne-ctedto rotate withsaid magnet and having a mass substantially less than the mass of saidmagnet, said armature having a second clutch surface composed ofnonmagnetic material and being adapted to engage said first clutchsurface on said clutch ring, said armature adapted to create a magneticfield opposing the magnetic field of said magnet so that electriccurrent passing through said armature causes said second clutch surfaceto engage said first clutch surface,

(d) said clutch ring having a mass less than said armature, and

(e) a drum accelerator means adapted to act independently of said clutchsurfaces and to contact and accelerate said drum means before saidcompliant coupling controls the speed of rotation of said recordingdrum. 10. In a recording system as set forth in claim 9 wherein the drumaccelerator means is electrically actuated and there is an electricalswitching means connecting said armature and said drum accelerator sothat both are actuated simultaneously.

References Cited by the Examiner UNITED STATES PATENTS DAVID J.WILLIAMOWSKY, Primary Examiner.

1. IN A RECORDING SYSTEM OF THE CLASS WHEREIN RECORDING OPERATIONS ARECOMMENCED AS A DRUM IS ACCELERATED FROM A STATIONARY POSITION, THEIMPROVEMENT COMPRISING IN COMBINATION. (A) A ROTATABLE RECORDING DRUMMEANS (B) A HIGH SPEED CLUTCH MEANS, (C) A COMPLIANT COUPLING MEANSCONNECTING SAID HIGH SPEED CLUTCH MEANS TO SAID DRUM MEANS, (D) A DRUMACCELERATOR MEANS ADAPTED TO ACT INDEPENDENTLY OF SAID CLUTCH MEANS ANDTO CONTACT AND ACCELERATE SAID DRUM MEANS, AND (E) A SWITCHING MEANSCONNECTING SAID CLUTCH MEANS TO SAID DRUM ACCELERATOR MEANS.